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| public static String ConvertBase(int from, int to, String s)
{
//Return error if input is empty
if (String.IsNullOrEmpty(s))
{
return ("Error: Nothing in Input String");
}
//only allow uppercase input characters in string
s = s.ToUpper();
//only do base 2 to base 36 (digit represented by characters 0-Z)"
if (from < 2 || from > 36 || to < 2 || to > 36)
{ return ("Base requested outside range"); }
//convert string to an array of integer digits representing number in base:from
int il = s.Length;
int[] fs = new int[il];
int k = 0;
for (int i = s.Length - 1; i >= 0; i--)
{
if (s[i] >= '0' && s[i] <= '9') { fs[k++] = (int)(s[i] - '0'); }
else
{
if (s[i] >= 'A' && s[i] <= 'Z') { fs[k++] = 10 + (int)(s[i] - 'A'); }
else
{ return ("Error: Input string must only contain any of 0-9 or A-Z"); } //only allow 0-9 A-Z characters
}
}
//check the input for digits that exceed the allowable for base:from
foreach (int i in fs)
{
if (i >= from) { return ("Error: Not a valid number for this input base"); }
}
//find how many digits the output needs
int ol = il * (from / to + 1);
int[] ts = new int[ol + 10]; //assign accumulation array
int[] cums = new int[ol + 10]; //assign the result array
ts[0] = 1; //initialize array with number 1
//evaluate the output
for (int i = 0; i < il; i++) //for each input digit
{
for (int j = 0; j < ol; j++) //add the input digit
// times (base:to from^i) to the output cumulator
{
cums[j] += ts[j] * fs[i];
int temp = cums[j];
int rem = 0;
int ip = j;
do // fix up any remainders in base:to
{
rem = temp / to;
cums[ip] = temp - rem * to; ip++;
cums[ip] += rem;
temp = cums[ip];
}
while (temp >= to);
}
//calculate the next power from^i) in base:to format
for (int j = 0; j < ol; j++)
{
ts[j] = ts[j] * from;
}
for (int j = 0; j < ol; j++) //check for any remainders
{
int temp = ts[j];
int rem = 0;
int ip = j;
do //fix up any remainders
{
rem = temp / to;
ts[ip] = temp - rem * to; ip++;
ts[ip] += rem;
temp = ts[ip];
}
while (temp >= to);
}
}
//convert the output to string format (digits 0,to-1 converted to 0-Z characters)
String sout = String.Empty; //initialize output string
bool first = false; //leading zero flag
for (int i = ol; i >= 0; i--)
{
if (cums[i] != 0) { first = true; }
if (!first) { continue; }
if (cums[i] < 10) { sout += (char)(cums[i] + '0'); }
else { sout += (char)(cums[i] + 'A' - 10); }
}
if (String.IsNullOrEmpty(sout)) { return "0"; } //input was zero, return 0
//return the converted string
return sout;
} |
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